1. Field of the Invention
The present invention relates to a ball joint apparatus used in mechanical element connection portions and the like of various machines. More particularly, the present invention relates to a technique capable of reducing a vibration/sliding torque and an elastic lift.
2. Description of the Related Art
In a vehicle stabilizer, a stabilizer bar is coupled with suspension devices of a vehicle, and the vehicle stabilizer has a function of stabilizing a posture of a vehicle using torsional reaction force of the stabilizer bar. For example, in a vehicle stabilizer, both ends of the stabilizer bar formed in a U-shape are coupled with operation portions of the suspension devices, and torsion portions of the stabilizer bar are fixed to fixing members of a vehicle frame, so that it is configured to receive the torsional reaction force.
A ball joint apparatus for connecting a stabilizer, a strut, arms and the like is used as an apparatus constituting a vehicle stabilizer (see, for example, Japanese Patent No. 3168229 and Japanese Patent No. 3369659).
FIG. 7 is a cross-sectional view illustrating an example of a ball joint apparatus. As illustrated in FIG. 7, the ball joint apparatus 310 comprises a rod member 311 and housings 312 integrally provided at end portions of this rod member 311. Deformation edge portions 314 are respectively provided at both right and left side portions of the rod member 311.
As illustrated in FIG. 8, the housing 312 includes a ball seat insertion unit 320 drawn into a cylindrical shape and a bottom surface 321 located at an end portion of the ball seat insertion unit 320. A flange portion 323 is provided at an opening portion of the ball seat insertion unit 320. A plurality of holes 324 are punched through the bottom surface 321.
A ball seat 330 is accommodated in the ball seat insertion unit 320. This ball seat 330 is made of a thermoplastic synthetic resin, and includes a recessed spherical surface 331 and an external peripheral surface 332.
A spherical head portion 341 of a stud ball 340 is engaged with the recessed spherical surface 331 of the ball seat 330 in a rotatable manner. The stud ball 340 includes not only the spherical head portion 341 but also a screw portion 342 and a large diameter portion 343, and a dust cover 345 is provided between a flange portion 344 and the large diameter portion 343 of the ball seat 330.
In the ball joint apparatus thus configured, as the suspension of the vehicle moves for a stroke, the stud ball 340 and ball seat 330 make vibrating/sliding movement. The characteristic during the swing/sliding movement is defined as a swing/sliding torque or a swing movement torque and a rotation torque.
The internal diameter of the inner peripheral surface of the housing 312 is formed to be less than the external diameter of the external peripheral surface of the ball seat 330, so that the ball seat 330 is sufficiently fixed within the housing 312 using elastic force. A difference between the internal diameter of the inner peripheral surface of the housing 312 and the external diameter of the external peripheral surface of the ball seat 330 is called as a tightening margin.
In recent years, demand to reduce suspension friction has increased in order to improve the riding comfort of vehicles, and it is required to reduce the swinging/sliding torque of the ball joint apparatus, i.e., one of suspension components. When the tightening margin is large, the ball seat 330 is pressed to the inside by the housing 312, and this reduces the clearance between the ball seat and the stud, and increases the swinging/sliding torque (for example, 1.6 Nm or more), which deteriorates the riding comfort. Therefore, a low-torque-type ball seat (for example, 1.0 Nm or less) that improves the riding comfort by reducing the tightening margin is considered.